A variety of work machines can be equipped with tools for performing a work function. Examples of such machines include a wide variety of loaders, excavators, telehandlers, and aerial lifts. A work vehicle such as backhoe loader may be equipped with a backhoe tool, such as a backhoe bucket or other structure, for excavating and material handling functions as well as a loader tool such as a loader bucket.
In the backhoe portion of the backhoe loader, a swing frame pivotally attaches to the vehicle frame at a rear portion of the vehicle, a backhoe boom pivotally attaches to the swing frame, a dipperstick pivotally attaches to the backhoe boom, and the backhoe tool pivotally attaches to the dipperstick about a backhoe tool pivot. A vehicle operator controls the orientation of the backhoe bucket relative to the dipperstick by a backhoe tool actuator. The operator also controls the rotational position of the boom relative to the vehicle frame, and the dipperstick relative to the boom, by corresponding actuators. The aforementioned actuators are typically comprised of one or more double acting hydraulic cylinders and a corresponding hydraulic circuit.
In the loader portion of the backhoe loader the loader boom is pivotally attached to the vehicle frame at a front portion of the backhoe loader and a loader tool, such as a loader bucket, is pivotally attached to the loader boom at a loader bucket pivot. Typically, the bucket is operatively attached to a linkage which is also connected to the vehicle frame or the boom. Work operation with a loader bucket entails similar problems to those encountered in work operations with the backhoe bucket.
During a work operation with a loader tool, such as lifting, lowering or dumping material, it is desirable to maintain an initial orientation relative to the frame of the vehicle to prevent premature dumping of material, or to obtain a constant loader tool angle. In conventional backhoe loaders, the operator is required to continually manipulate a loader tool command input device to adjust the loader tool orientation as the loader boom is moved during the work operation to maintain the initial loader tool orientation relative to the vehicle frame. The continual adjustment of the loader tool orientation, combined with the simultaneous manipulation of a loader boom command input device, requires a degree of operator attention and manual effort that can diminish overall work efficiency and increase operator fatigue.
A number of mechanisms and systems have been used to automatically control the orientation of work tools such as loader buckets. Various examples of electronic sensing and control systems are disclosed in U.S. Pat. Nos. 4,923,326, 4,844,685, 5,356,260, 6,233,511, and 6,609,315. Control systems of the prior art typically utilize position sensors attached at various locations on the work vehicle to sense and control tool orientation relative to the vehicle frame. Additionally, the U.S. Pat. No. 6,609,315 makes use of an angular velocity sensor attached to the tool to sense and maintain a fixed work tool orientation relative to an initial tool orientation, independent of vehicle frame orientation. Also, U.S. Pat. No. 7,222,444, makes use of a tilt sensor that, when attached to an object, such as the tool, detects the object's inclination with respect to the earth.